This invention relates to release coating compositions for pressure sensitive adhesives. More particularly, this invention relates to thermosetting, resinous release coating compositions which do not employ organic solvents. Said compositions are characterized by their ability to provide for the rapid peeling of cover sheets from labels and the like and, for the rapid unwinding of tapes and other adhesive bearing materials in roll form.
As is known in the art, the use of pressure sensitive adhesives and, at times, that of non-pressure sensitive adhesives calls for the use of a release coating. In the case of the pressure sensitive materials, if tape, the release coating is applied to the side opposite that to which the adhesive layer is affixed, or, if in sheet form whether label or bandaid or "contact paper" or the like, the release coating is applied to that side of the protective cover sheet which comes in contact with the adhesive layer.
Conventional release coating compositions are usually film forming substances or solutions essentially comprised of a solvent, a release agent, and, at times, one or more optional additives. Among the more prevalent conventional release coating compositions are included those which are essentially comprised of a thermosetting silicone resin dissolved in an organic solvent such as toluene or xylene or the like. Release coating compositions of this type have proven quite useful in providing for the rapid release of cover sheets of labels and the like and, for the easy unwinding of tapes and other adhesive bearing articles in rolled form. However, they often present problems such as fire hazards and pollution, due to the presence of the solvent, and, in particular, the transfer or migration of the silicone into the adhesive layer. This undesired occurrence of silicone migration, which usually happens during storage of the coated product, is especially evidenced by a significant decrease in adhesive strength, due to the contamination of the adhesive layer.
Heretofore various efforts have been put forth to overcome the silicone migration problem. For example, a well known method is to first coat the cover sheet or interleave liner or the back side (non-adhesive bearing side) of the tape substrate with an anchor layer prior to applying the release coating. Another method is to use extremely low amounts of silicone and increased amounts of surfactants. Though such methods have proven to be somewhat successful, they are, in some respects, impractical or of limited usefulness. For instance, the use of an anchor layer presents an added cost factor and calls for the additional steps of preparation and coating. On the other hand, the use of too low an amount of the release agent, i.e., lubricant with increased amounts or surfactants, may result in inadequate or very poor separation from the adhesive layer and concomitant surfactant migration. For the foregoing reasons, there exists a need for a release coating composition which does not call for the use of an organic solvent and is capable of overcoming the inherent shortcomings of the prior art compositions.